1. Technical Field
This disclosure relates in general to using plasma actuators to manipulate jet exhaust flow. This disclosure relates in particular to using dielectric barrier discharge plasma actuators on the surface of jet nozzles to improve nozzle thermal environment, reduce acoustic noise and increase propulsion system performance.
2. Description of Related Art
Jet engine exhaust nozzles must withstand severe thermal and acoustic effects. High temperatures and thermal gradients in the exhaust system reduce durability of nozzle materials and structures. High velocity exhaust flows, especially in the presence of dynamic flow separation and reattachment, result in severe jet noise. This can be an issue from the ground environment point of view (takeoff noise regulations, ground crew safety, etc) as well as having aircraft structural/acoustic implications. Thermal issues have traditionally been addressed by mixing cooler flow with hot flow or by introducing a film of cooling air along the surface to be cooled. However, the propulsion system performance penalty associated with the large amount of cooling air which may be necessary can have an adverse impact on vehicle performance. Noise reduction approaches have also included mixing cooler air with hot engine exhaust as well as the use of tabs, lobes, or deformable geometry to promote mixing. These approaches can also introduce performance penalties as well as weight and complexity. A means of manipulating the exhaust system flow field to alleviate thermal and acoustic concerns with lower performance penalties, weight and complexity than traditional approaches is needed.
Some development has considered localized arc filament plasma to manipulate exhaust flowfields for noise reduction. Arc filament plasma produces an electric arc between two electrodes, which produces rapid local heating of flow in the vicinity of the arc. This produces a rapid pressure rise and a shock wave which propagates radially from the arc into the surrounding flow. Arc filament plasma may complicate exhaust system cooling because of the large amount of heat generated by the arc.
Nozzles for high performance aircraft typically operate off-design at takeoff and low speed conditions, thus incurring decreased efficiency. Elimination of this performance penalty with current approaches would require the use of increased variable geometry. But this would incur additional complexity and weight. A more efficient means of reducing nozzle off-design performance penalties is needed.
Thrust vectoring exhaust systems offer improved vehicle survivability, maneuverability and the opportunity to reduce the size of air vehicle aerodynamic control surfaces. Mechanical vectoring nozzle systems, however, incur increased complexity and weight which can adversely impact vehicle performance. Fluidic vectoring exhaust systems provide thrust vectoring with less complexity and lighter weight, but may result in reduced non-vectoring thrust performance. Conventional fluidic vectoring systems require a supply of high pressure gas from the engine or some other source. This can result in vehicle propulsion system performance penalties. The injection orifices in nozzle surfaces also pose challenges from a survivability, producibility, and maintainability perspective. A means of manipulating exhaust system flowfields to vector engine thrust is needed which is mechanically simple, durable, light weight, and imposes less penalty on propulsion system and vehicle performance.